Racers are always looking for ways to make their dirt bike go faster. I’ll admit, it awesome to have a bike that absolutely rips…. I hate to break it to you, but if you can’t handle the bike on the track, there’s not much use to having the fastest dirt bike in the world, unless of course you’re straight line drag racing against your pansy friends with quads.
A pretty much stock bike that is properly set up for your weight, height, riding style, experience, and riding terrain will be far better than one that’s cranking out 50% more horsepower than everyone else (It will also be more reliable!).
Whether you’re doing Motocross racing, hare-scrambles, enduros, or flat-track, if you’re suspension isn’t set-up right it’s not going to perform nearly as well. You won’t be as fast and will get worn out quicker because you’re either getting thrown around from rock-hard suspension, or you’ll be bottoming out and bouncing everywhere from it being too soft.
It may cost quite a bit of your money to get your dirt bike re-valved and set-up for your riding style, especially if you have to get different springs for your weight. But, the reward is more than worth it… Your bike will ride so much smoother over obstacles, and you won’t get so beat up from the abuse, allowing you to ride harder for longer.
If your bike isn’t jetted correctly, it’s not going to run as well as it should, and could possibly lead to a blown engine. I realize that many of the new four-strokes are going to fuel-injected, but many people think that they don’t have to do anything if they make any modifications to the engine or exhaust. Some bikes come rich from the factory, so if you put an aftermarket pipe on it, the jetting may be pretty close to spot on. But if it was already jetted to spec, then modifications will cause the bike to run lean. The result will probably make the bike slower, and you will be slowly burning down your engine because it’s not getting enough fuel.
Too rich, though, and you will be wondering why you’re eating through spark plugs. Your dirt bike will cough, sputter, and act sluggish. So now you know that too lean of jetting is not healthy for the bike, and too rich is slower and cause problems. Some people may say that too rich is fine because it’s safer for your engine, but it’s really not because you will foul more plugs, and get more carbon build-up from the gas that’s not being burned. A finely-tuned, stock motocross bike will run much better and be more reliable than a highly modified bike that isn’t.
Aftermarket pipe, cams, porting, intake modifications, or even re-jetting aren’t going to help if your bike’s top-end is worn out. On a two-stroke motocross bike, this usually means that piston and ring(s), but on a four-stroke it could also have worn out or out of spec valves, timing chain, and tensioner. It all depends on what kind of riding you do and how hard you ride the bike, but a routine top-end rebuild/inspection is every 15-20 hours. A two-stroke should have a new ring installed every time you check it if you’re motocross racing. A piston can last anywhere from 15-50 hours depending on how it’s ridden.
Four-strokes have many more moving engine parts, so routine check-ups are crucial if you want the bike to last. Valves and timing chain should be checked every 15-20 hours because they can go out of spec in a matter of hours on certain bikes. A piston should last 20-40 hours of racing, but again, it depends on the rider and what kind of riding it is.
Before you do anything else, even jetting your bike, if your top-end hasn’t been checked or rebuilt in more than 20 hours, get on it! A fresh top-end is preventative maintenance, and it can bring back a couple ponies that you need to pass a rider.
Most stock motocross bikes come with a transmission and sprockets that are already geared well for racing. But, what if you get on a tight supercross-style track where you need to get out of corners faster to clear the next jump? That’s when it’s time to start messing with your sprockets!
Your goal for gearing is to able to rev the bike out in 4th, 5th, or 6th gear, depending on the track size. This means that if you’re in low-mid of 5th gear on the fastest part of a track, then you should re-gear it so that it’s in the meat of the power in either 4th or 5th gear. If it’s geared too tall then you’ll have to do more clutch work, and acceleration won’t be as good as it could be. Too low of gearing and you will be shifting too often.
Some people are confused when it comes to gearing, so let me explain what will happen when you change a sprocket. If you go down a tooth on the front sprocket (13 to 12), then the bike will accelerate quicker, but you’ll have to shift more and it won’t have as high of a top speed. The opposite will happen when you go a tooth larger on the front/counter-shaft sprocket (13 to 14). For the rear, if you go a tooth smaller (50 to 49), then the bike will have a higher top speed, and you won’t have to shift as often, but acceleration will be slower, and keeping it in the meat of the power will be more difficult. Vice-versa if you add a tooth to the rear. Also, don’t forget to adjust your chain when you change sprockets.
Ok, I know you’re probably thinking, “Why aren’t any performance parts on this list?!” Well, it’s kinda’ like what I previously said… A stock bike that’s finely-tuned and properly set up is faster than a bike with thousands of “hop-up” mods to make it go faster. You must realize that 90+% of racing is the rider and NOT the bike.
Anyway, the reason exhaust is even number five on this list is because they can change the power-curve to suit the rider and riding style. Exhaust systems are actually pretty good these days, so most bikes won’t gain much power from an aftermarket exhaust (yes, even after re-jetting it!). They usually move the power around more than anything (especially on two-strokes).
A pipe that offers more low-end to mid-range power is better for beginning riders and woods riding. For outdoor motocross tracks and riders that like to wring their bikes out, a pipe for top-end power is best suited. When looking for the right exhaust pipe, keep in mind that if you add power to one end of the RPM range, it will probably lose some on the other end.
Remember that these are my top 5 mods for a motocross bike. But if you ask any good rider that knows what they’re talking about, I could guarantee that their top 5 mods are most if not all of these as well. Good luck, and have fun racing!